1. Field of the Invention
This invention lies in the field of rotating biological contactors, particularly modular tankage systems for such apparatus.
2. Prior Art
Rotating biological contactors are used for the biological treatment of wastewater. Such a device characteristically utilizes a wastewater contacting medium which is fixed upon a rotatable shaft and arranged to continuously revolve in a reservoir of wastewater to be treated. In an aerobic such device, as the contacting medium rotates, the medium experiences alternatively exposure to wastewater and then to oxygen (air). A biological culture develops on the medium which has capability for digestion of substrates in the wastewater.
The rotating biological contactors has only been used in the United States since the early 1960's. The state of the art is presented in such publications as "Fixed Biological Surfaces--Wasterwater Treatment" by R. L. Antonie (CRC Press, 1976), "Biological Wastewater Treatment Theory and Application" by C. P. L. Grady, Jr., and H. C Lim (Marcel Dekker, Inc., 1980), and the "Proceedings: First National Symposium/Workshop on Rotating Biological Contactor Technology" edited by E. D. Smith, R. D. Miller, and Y. C. Wu (Army Corp. Engineers, USEPA, and University of Pittsburgh, 1980).
Currently, what is believed to be the most common commercially available form for a rotating biological contactor apparatus utilizes a single, horizontally rotatable shaft about 25 feet long which carries contacting media having a gross diameter of about 12 feet and which media provide a total of about 100,000 square feet of surface area. Commonly, such one shaft extends through a multiplicity of axially aligned stages or chambers (typically from 3 to 6 stages) and the contacting media are so distributed along the shaft as to locate portions thereof in each stage. Such a type or form of rotating biological contactor apparatus is also commercially available in a plurality of other sizes from various manufacturers. Thus, arrangements are believed to be commercially available wherein the diameters of the contacting media range from about 4 to 12 feet, and the number of individual stages in such apparatus ranges upwards from one.
Commonly, the tankage portion of a conventional large commercial apparatus is locally designed and built to accomodate a rotating contactor and associated shaft subassembly purchased from some manufacturer. Such a tankage portion is commonly fabricated on site of poured concrete. However, in all known commercial forms of such a rotating biological contactor apparatus the tankage portions are individually designed and manufactured either to order, or as packaged assemblies, and all such apparatus embodiments are either fixed, or are characterized by having very limited variablity, in operational configuration. The stationary components are dimensionally fixed.
Another type of commercially available rotating biologioal contactor apparatus employs a plurality of contactor/shaft assemblies wherein the shafts are in generally spaced, parallel relationship to one another with each shaft being supported over a separate but adjacent operational stage of a stage plurality with the stages arranged in a side-by-side manner. Here, no variation whatever in this fixed relationship between components, especially the stationary tankage components, appears to be possible once a given such apparatus embodiment is in place.
Particularly because of the many variations in application situations, a need has developed in the field for a type of rotating biological contactor apparatus which can be rapidly, simply reliably and inexpensively assembled, modified, and/or expanded even after an initial installation has been completed and operated. A plurality of various potential apparatus configurations would be desirable using the same subcomponents for assembly. The capability for using the same apparatus subcomponents in the assembly of a variety of different rotating biological contactors would, if available, offer many practical advantages, especially for treating a variety of wastewaters, such as, for example, those having (a) a relatively low level of pollutants, (b) a relatively low flow characteristic, and (c) a relatively significant compositioned change (by comparison to an initial compositioned condition).